For patients who are starting to take antiretroviral medication (to treat HIV) for the first time, there are now a variety of different medicines which may be taken together as a combination in order to form an effective treatment which suppresses the virus for prolonged periods of time. Currently, national guidelines recommend the use of two different drugs of one type (the nucleoside/ nucleotide reverse transcriptase inhibitors, NRTI often known as "nukes") with a third drug from one of two other types (either a nonnucleoside reverse transcriptase inhibitor, known as an NNRTI or "nonnuke", or a protease inhibitor, known as a PI) to form a treatment regime of three active drugs. In the UK and Europe, all PIs are given in combination with a small dose of a second PI, ritonavir, which has the effect of boosting the levels of the active PI in the bloodstream.